This simplifies a few operations and removes the size limitations
implied by the message buffer used.

Change-Id: I8b873a0ffa399a037ff5c2501ba4b68158810968
Reviewed-on: https://chromium-review.googlesource.com/724285
Commit-Queue: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#48766}